One vertex per element, one color per generator, with an edge from x to x·s.
(1,2)(3,7)(4,6)(5,8)(9,10)(11,17)(12,15)(13,16)(14,20)(18,22)(19,23)(21,24)(25,26)(27,33)(28,36)(29,30)(31,35)(32,37)(34,38)(39,40) involution — undirected(1,2,4,6)(3,5,8,7)(9,11,15,13)(10,16,12,17)(14,21,22,19)(18,24,20,23)(25,27,30,35)(26,31,29,33)(28,34,37,40)(32,38,36,39)(1,2)(3,5)(4,6)(7,8)(10,12)(16,17)(18,20)(23,24)(28,37)(32,36)(34,40)(38,39) involution — undirected(1,3)(2,5)(4,8)(6,7)(9,12,15,10)(11,17,13,16)(14,20,22,18)(19,24,21,23)(25,28,30,37)(26,32,29,36)(27,34,35,40)(31,38,33,39)(9,13,15,11)(10,17,12,16)(14,21,22,19)(18,24,20,23)(25,29,30,26)(27,31,35,33)(28,36,37,32)(34,38,40,39)(9,14,15,22)(10,18,12,20)(11,19,13,21)(16,23,17,24)(25,27)(26,33)(28,34)(29,31)(30,35)(32,39)(36,38)(37,40)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.